Usually, the volume consumed by a layered electrical device or assembly, such as a printed circuit board, or integrated circuit chip, is a very valuable commodity in the design of an electronic assembly device. The volume of the assembly dictates the number, size, and placement of components on it. In addition, with the advent of personal computers, a major limitation is in the space available for components to exist above the actual device surface. For example, minimization of the space used above the actual device represents a minimization of volume used for a system of printed circuit boards connected to a common bus, and thus maximizing the use for that volume.
The area of a surface consumed by mounted devices on a circuit board is also a very valuable commodity. Therefore, to reduce the surface area used by a mounted device lets the designer use that much more surface area for additional functional devices. Specifically, if one could redesign a circuit board with all the electric storage devices embedded within the board, a designer could use much more surface area for additional functional devices on that circuit board. Or, the designer could reduce the entire assembly size.
Similarly, if an integrated circuit chip (IC chip) could embed smaller, more powerful electric storage devices within the layers making up the chip, more volume of the chip could be dedicated to other functional purposes.
Typically, in a printed circuit board, the design of the circuitry requires some sort of energy storage device, such as a capacitor or battery. The designer usually chooses a discrete component for such a storage device in the circuit. This discrete component occupies surface area of the board and an amount of volume in and above the board.
During the printed circuit board manufacturing process, the spot where the energy storage device is to be placed is left blank for attachment later. Usually, a manufacturer manufactures the circuit board with holes placed where the leads of the storage device will be attached. Later, a discrete electrical storage device, such as a battery or capacitor, is placed into the circuit and electrically attached to the circuit board with a secondary interconnection such as a screw on contact or soldered joint. Usually, the circuit connections are terminated at the hole where the storage device leads will be placed, and when the storage device leads are guided into the hole, this completes the circuit path.
However, using discrete electrical storage device components has several drawbacks. One main drawback is that most of the electrical storage device components and the necessities for their connection to the circuit take up valuable surface area on and occupy volume in and above the board.
With respect to IC chips, large electrical storage devices are impracticable. First, usually an IC chip usually does not have any interconnections to discrete devices through its surface. Second, the small volume of a chip does not lend itself to large or medium electrical storage devices.
Generally, capacitors in particular require large areas and volumes, and tend to tower above other components on a board. Even smaller capacitors on a circuit board can be the tallest components on a board. Capacitors present design problems due to placement, and take up valuable board surface area and volume.
The equation (k.times.A)/T defines the capacitance of an energy storage device, or a measure of the amount of electric charge it can hold. In the equation, k stands for the dielectric constant of the material between two opposite charged plates, A being the area of the smallest plate, and T being the thickness of the dielectric material. Thus, small volumes and areas, without a high dielectric constant, make smaller capacitances. For very small volumes and areas, such as in an IC chip, large storage devices are impracticable due to space limitations and the fact that most IC chips do not provide for a surface interconnection to other discrete components.
If a design requires a larger capacitor in a particular, the problem is amplified further. A larger capacitor tends to require a larger area and volume to house the discrete component. Usually, for printed circuit boards, the solution is to place the capacitors where they extend outward from the board.
An example of the space needed for capacitance can be shown in the context of a power supply, where capacitors can take up about 30% of a board's space.
Another problem exists when the discrete storage device must be interconnected into the circuit board. Usually, a manufacturer must solder all components into a connection to the circuit in the printed circuit board. This interconnection is a weak point and the cause of many failures in printed circuit board packages. The interconnection is also a point where manufacturing mistakes can occur. Thus, an energy storage device integrated directly into the layers of a layered electrical device, such as a printed circuit board or IC chip, is very valuable.
In an integrated circuit chip, the spaces involved are so small that significant capacitance or energy storage is not possible. The only place to put any energy storage device is in the substrate comprising the integrated circuit chip. Thus significant energy storage, as a battery or capacitor, is untenable for these devices.
What is needed is an apparatus in which the energy storage device components do not take up area on the surface of and volume above a layered electrical device. If this could be achieved, this would free up valuable area for the placement of components and free up the volume used by discrete components. In addition, an integrated electrical energy storage device formed in the substrates of an IC chip could greatly enhance the functionality of that chip. Further, an integrated energy storage device in a layered electrical device is needed to enhance semiconductor performance, since it eliminates some soldered connections.